Field of the Invention
The invention relates generally to power subsystems for downhole equipment such as electrical submersible pumps (ESP's), and more particularly to means for cooling electric drive systems in harsh environments while preventing introduction of contaminants into the drive systems.
Related Art
Downhole equipment such as ESP systems are commonly installed in wells for purposes of producing fluids (e.g., oil) from the wells. Typically, AC power from an external source such as a power grid is converted by an electric drive system to DC power, which is in turn converted to AC power that is suitable to drive the downhole equipment. This AC power is delivered to the equipment via power cables that extend into the wells.
The electric drive for an ESP system is normally located at the surface of the well. Heat generated by the drive in the process of rectifying the input power and producing the AC output power is typically dissipated by circulating ambient cooling air through the drive. In some cases, wells are drilled in locations such as deserts, where there may be a great deal of sand and dust in the ambient air that is circulated through the drive. The sand and dust may accumulate in the drive, reducing its ability to dissipate heat.
Conventionally, this problem may be addressed by implementing a thermoelectric cooling system to help dissipate the generated heat. These systems, however, require constant power input to provide a cooling effect, and they are notoriously inefficient, so they consume large amounts of power to remove nominal amounts of heat. Although not implemented in current systems, it would be possible to provide a system that uses a working fluid and turbomachinery, such as a vapor-compression system, to cool the drive components. While this type of cooling system would likely be more efficient than a thermoelectric system, it would be much more prone to maintenance, which would be undesirable. Another option that is not currently used would be to filter the ambient air before it is circulated through the drive. In some cases, however, a portion of the sand and dust particles are small enough that they cannot be easily filtered out of the ambient air. Filters that are capable of eliminating these fine particulates would typically impede the flow of the cooling air, making this an impractical solution.
It would therefore be desirable to provide an inexpensive, efficient, low-maintenance thermal management solution for sealed electric drive systems that must operate in contaminated environments for prolonged periods of time.